Keelson /(?)/

Keel·son

Keelson

n.
  1. A piece of timber in a ship laid on the middle of the floor timbers over the keel, and binding the floor timbers to the keel; in iron vessels, a structure of plates, situated like the keelson of a timber ship. (Shipbuilding)

Phrases & Compounds
Cross keelson
a similar structure lying athwart the main keelson, to support the engines and boilers.